Transcript File

Strange Rocks
C1.3
The Plan
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Review 1.3 Strange Rocks
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Activity
1.4 Getting a Handle on Time
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Song
Definitions
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Stratigraphic sequence: a sequence of rocks that provides a
chronological record of a region’s geological history
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Relative dating: the process of placing rocks & geological
structures in the correct chronological order
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Absolute dating: the exact time that has elapsed since an
event occurred
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Intrusion: a body of rock that forms from the invasion of
magma into a pre-existing rock formation. An intrusion is
younger than the pre-existing rock it moved into.
Formation of Sedimentary Rock
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Step 1: Rivers transport sediment which contains fossils.
Step 2: Over time additional strata are added.
Step 3: Sedimentary rock is exposed when the sea floor is
pushed up or by erosion.
What are the 5 principles used for relative
age?
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2.
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5.
The Principle of Uniformitarianism: What is
happening now, happened in the past.
The Principle of original horizontality: A new layer
is placed horizontally over an older layer. Folds or tilts
indicate a geological event.
The Principle of Superposition: The layers become
younger as you move to the top. Layer A is the
youngest.
The Principle of Cross-cutting: Disruptions (like
intrusions or faults) are younger than the layers they
disrupt or cut through.
The Principle of Faunal succession: Layers of rock
with similar fossils or rocks are the same relative
ages – the age in terms of older or younger than.
Well known fossils that lived a short time are good for
age of rock and are called index fossils.
Geological Time Scale
Geological time of earth is separated into three units:
1. ERAS: Large units of time determined by major global
environmental or geological changes. There are four eras –
Precambrian, Paleozoic, Mesozoic & Cenozoic.
1.
PERIODS: are units of time within each era symbolized by
regional changes.
1.
EPOCHS: are the small units of time within the Cenozoic
Era which are based upon the rise and fall of sea levels.
The Grand Record
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The Earths time scale is
divided into
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4 Eras: Precambrian,
Paleozoic, Mesozoic &
Cenozoic (massive
dissappearances of fossils
and appearance of new
fossils mark the boundary
between each era.)
Cenozoic Era
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extinction of non-avian dinosaurs to the present.
called the “Age of Mammals, Flowering Plants, Insects, Fish
& Birds".
divided into two PERIODS:
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the Quaternary Period (present) which has two Epochs
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Holocene Epoch (present)
Pleistocene Epoch
the Tertiary Period.
Mesozoic Era
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Dinosaurs alive; A time of great change in the
terrestrial vegetation
Means "middle animals“
Divided into three Periods:
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Cretaceous
Jurassic
Triassic
Paleozoic Era
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Multi-celled animals underwent a dramatic "explosion" in
diversity; Six continents experienced mountain building; It
ended with the largest mass extinction in history wiped out
approximately 90% of all marine animal species.
Divided into six periods:
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Permian
Carboniferous
Devonian
Silurian
Ordovician
Cambrian
Precambrian Era
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Makes up roughly seven-eighths of the Earth's history; the
Earth formed, life arose, tectonic plates moved,
cyanobacteria evolved, atmosphere filled with oxygen, the
first animals, evolved
Recall: The Law of Superposition
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Law of Superposition: higher strata (layers) in a
sequence of rock layers are younger than lower strata
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the oldest rock is at the bottom of the sequence and the most
recent layer is at the top.
Which type of fossil dating uses this law, absolute dating,
or relative dating?
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relative dating - the process of placing rocks and geological
structures in the correct chronological order based on their
relative position
Practice Problem
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The following drawings represent the steps required to
make tonguestone. Put them in order from first to last.
How can fossilized shark teeth become
imbedded in rock that is on land high
above sea level?
A shark living in an
ancient ocean sheds
its teeth.
The teeth sink to the
bottom of the ocean
and are buried in
fluid sediment.
Over time, the
sediment hardens
and becomes
sedimentary rock.
How can fossilized shark teeth become
imbedded in rock that is on land high above
sea level?
Over time, more
and more layers
are deposited and
the sea level drops
or the layers are
lifted to become
dry land.
Erosion creates an
outcropping,
exposing part of
the layer.
The site is excavated
to expose the
fossils.
What can be fossilized?
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Any organic material that is “hard”. This includes
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shells,
teeth,
bones,
corals,
diatoms
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just to name a few….
How can something be fossilized?
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One process involves the item being buried, especially
somewhere there is minerals (one such place is in or
by a water source). Then over many years the
minerals seep into the pores of the “hard” parts,
which over time replaces the actual “hard” part to
create a mineralized form of the “hard” part.
Another process involves the item being buried and
then compressed into the rock layers beneath it. And
over time the organism decays and what’s left behind
is an impression of itself.
Smith’s Observations
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William Smith noticed that certain distinctive fossils kept
re-appearing at each surveyed location.
Further, these distinctive fossils always appeared in the
same order within the layers of rock at each location.
So what does this mean?
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If a distinctive fossil existed only for a limited period of
time, then rocks containing that fossil must correspond
closely in age with other rocks that contain that same
fossil.
These distinctive fossils are like an index; they establish a
common time of origin for widely dispersed rock layers.
That’s why these fossils are called index fossils.
Index fossils:
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a fossil used to determine the relative age of a layer in a
stratigraphic sequence or to match stratigraphic sequences from
different locations
they are the better preserved fossils and are from a very shortlived species which is known to have existed during a specific
geological time period
How does an index fossil work?
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scientists would use their different processes of dating to put a
particular age to an index fossil.
when they come across a rock layer that contains that particular
index fossil they would know the approximate age of the rock layer
no matter where they found in it the world.
Practice Problems:
1.
2.
3.
Determine the oldest
layers of rock at
Location 1 and 2.
Determine the youngest
layers of rock at
Locations 1 and 2.
Conclude which layer in
Location 1 contains rock
of roughly the same age
as the rock in layer X of
Location 2.
Activity
Can stratigraphic sequences from different locations be matched
by using index fossils to form on larger sequence?
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Step 1: Use the scissors to cut out the eight fossil cards
from the handout.
Step 2: Place the fossil card with the letter M in the
lower left-hand corner of your workspace. This
represents the oldest rock layer, so it is on the bottom.
Step 3: Find a rock layer on a fossil card that contains at
least one of the fossils you found in the oldest rock layer.
This rock layer is younger, as indicated by the presence of
a new fossil species. Place this rock layer above the oldest
rock layer.
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Step 4: Repeat the process outlines in step 3 to select
a fossil card to be the third rock layer.
Step 5: Check your work. If a fossil is present in layer
1, it should NOT disappear from layer 2 and then reappear in layer 3. Since extinction is forever, once a fossil
disappears from the fossil record it does not return. If
necessary, re-adjust the fossil cards you chose for layers
2 and 3.
Step 6: Repeat the previous three steps for each of the
remaining fossil cards. When you are finished you
should have the rock layers assembled into a
stratigraphic sequence.
Activity (solution)
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The correct sequence from youngest to oldest spells out
the word organism.
More on index fossils:
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Graptolite, placoderm, and ammonite are the most
suitable index fossils because they are only found during a
short amount of geological time.
A good index fossil:
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Appears only briefly in the geological record
Has a wide geographical distribution
Is easily recognizable.
Wealth from Ancient Seas
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Fossils are not just important for geological
dating – they also form the primary fuel we rely
upon in Alberta
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Geologists suspect most of Alberta became submerged
at the bottom of a tropical sea by the end of the
Ordovician Period.
Over the next 200 million years, sea levels rose and fell
When it was submerged, Alberta became the home to a
now extinct group of sponges.
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These sponges secreted a brittle calcium carbonate skeleton
that, together with coral, became the main component of
huge reefs that eventually occupied hundreds of square
kilometres of the underwater environment.
these porous reefs were 10-storeys tall in some places, and
became the storage containers for life that would later form
our petroleum reserves
Making Petroleum
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Over the next 200 million years microscopic
marine organisms—mostly plankton—had been
living and dying in the warm tropical seas that
often covered most of Alberta.
Geologists suspect that the dead plankton
remains created thick blankets of organic ooze
that fell to the bottom of the sea to become a
food source for bacteria.
The bacteria were thought to have removed most
of the oxygen and nitrogen from this organic
matter to leave mostly carbon and hydrogen,
which are the main ingredients of petroleum
Making Petroleum
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During the next 380 million years, this layer of
organic material was subjected to heat and
pressure that encouraged chemical reactions to
occur
Thousands of metres of sediment were piled on
top.
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The accumulated top layer of sediment eventually
changed into rock.
Once the hydrocarbons had been converted into
liquids, the pressure from above pushed these
materials into more porous rock—the fossilized
remnants of the ancient reefs.
Since the type of rock formed above and below
the reservoir of petroleum was impermeable
shale, the petroleum had no place to go.
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This is why a large concentration of petroleum in
subsurface rock is called a petroleum trap.
The Burgess Shale
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In Chapter 2 you have been introduced to three fossils: a
trilobite, Canadia, and Hallucigenia. Samples of all three
fossils have been found in the shale on the side of Mount Wapta,
about 80 km west of Banff. This location is known as the
Burgess Shale, and it’s considered by many scientists to be
the most important source of Cambrian fossils on Earth.
Geologists have evidence that more than 500 million years ago,
the organisms now fossilized in the Burgess Shale were
inhabiting a shallow area close to the shore of a tropical sea.
The Burgess Shale
Matching Rock Strata from Different
Locations
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Pg. 311
Can stratigraphic sequences from different locations be
matched by using index fossils to form one larger
sequence?
Assignment
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Add the events in the section to your time line
Practice Questions
1.3 Questions
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Pg. 313 #1-10